Imma Perfetto
Cosmos science journalist
How do you eat your Oreos?
Perhaps you twist the top layer, separating the cookie into two parts, and then eat them one by one. Alternatively, do you dunk the biscuit into milk to soften it just the right amount? Or maybe you just shove the entire thing in your mouth, all for efficiency of course.
Snacking on an Oreo while testing its mechanical properties in the lab is apparently a legitimate methodology of research, according to a team of rheologists – physicists who study complex fluids – from Massachusetts Institute of Technology in the US.
In a cookie-breaking new study, the authors have introduced an emerging field called “Oreology”, derived from the Nabisco Oreo for cookie and the Greek rheo logia for “flow study”. It’s the study of the flow and fracture of sandwich cookies and the research has been published in the journal Physics of Fluids.
Oreo creme is a member of the class of flowable soft solids known as “yield stress fluids,” which are fluids that act as soft solids when undisturbed and only flow under a sufficiently large amount of applied stress.
The researchers characterised the flow and fracture of Oreos, finding that the creme – which they’ve found is “mushy” in rheological texture – tends to stick to just one side of the cookie.
“Rheology can be used to measure the texture of food depending on the failure stresses and strains,” says first author Crystal Owens, a graduate student in the Department of Mechanical Engineering at MIT. “We were able to characterise Oreo creme as quantitatively mushy.”
The team used a laboratory rheometer – an instrument which characterises the flow of a substance in response to forces – to measure the fail mechanics of an Oreo’s filling. The rheometer fixed one side of the cookie in place and carefully twisted the other until the filling failed and the cookie broke apart, after which the amount of creme on each wafer could be determined by visual inspection.
“I had in my mind that if you twist the Oreos perfectly, you should split the creme perfectly in the middle,” says Owens. “But what actually happens is the creme almost always comes off of one side.”
In fact, nearly all of the creme (95%) remained on just one of the biscuits after breaking, and it seems that the production process is the likely cause. Within the boxes tested, 80% of cookies had creme–heavy sides oriented uniformly in one direction, rather than 50% as would be expected from random chance.
In a thorough investigation of this phenomenon, the rheologists also tested the influence of rotation rate, amount of creme, and flavour on the post-mortem creme distribution.
After being dipped in milk, the Oreos degraded quickly, crumbling after about 60 seconds. Flavour and filling seemed to have little effect on the cookie mechanics but breaking the cookies apart cleanly did depend on the rotation rate.
“If you try to twist the Oreos faster, it will actually take more strain and more stress to break them,” Owens advises. “So, maybe this is a lesson for people who are stressed and desperate to open their cookies.
“It’ll be easier if you do it a little bit slower.”
The team encourages further contributions to this emerging field of study but acknowledges the fact that a laboratory rheometer is not widely accessible.
But the researchers have come up with a way to overcome this hurdle, thanks to a design for an open–source 3D–printed “Oreometer” – a rheometer specially made for twisting Oreos – for use in higher-precision home studies.
Powered by rubber bands and coins, the team hopes to encourage educators and Oreo enthusiasts to continue studying the cookies and learning about rheology.
“One of the main things we can do with the Oreometer is develop an at-home education and self-discovery plan, where you teach people about basic fluid properties like shear strain and stress,” concludes author Max Fan, an undergraduate student at MIT.